This invention relates to the recovery of resinous materials from articles of commerce, and more particularly to the recovery of thermoplastic resins.
In recent decades, the number and variety of commercial applications for resinous materials has increased beyond all estimates, and presently accounts for the manufacture of a majority of all commercial products. The heavy employment of such resinous materials has resulted in a constantly growing demand for the raw material. As many of the starting materials for the manufacture of these resins are derived from naturally occurring commodities such as petroleum, the recent increase in the cost of petroleum, coupled with its finite supply, looms as a serious problem that could manifest itself in the future in the form of curtailed supplies and concommitant price escalations.
A second more immediate problem which likewise portends to reach critical proportions is the disposal of commercial articles prepared in whole or in part from these resinous materials, which articles are no longer useful. For example, a variety of products ranging from package wrapping materials and ball point pen barrels, to insulative coatings on metal conductors, must be effectively and economically disposed of in a way which minimizes negative environmental impact. Most synthetic resinous wastes are disposed in the same manner as other waste materials, and are thus incinerated or otherwise destroyed, and the residue then is disposed of in land fills and the like. The incineration of these materials presents dangers to the air quality of the adjacent area, as the by-products of incineration comprise a variety of toxic vapors that must be effectively recovered before they escape into the atmosphere.
Also, as the use of these resins in commercial products increases, along with the general increase in refuse that must be disposed of, the problem of availability of disposal sites will become critical. When the difficulties of the disposal of these materials is considered with the eventuality that these materials may become less available and more expensive due to a reduction in the natural resources from which the starting materials of these resins are derived, the importance in value of recovering these materials from spent commercial applications becomes increasingly important.
The prior art is aware of several solvent compositions that have been utilized in the past for stripping certain resinous coatings from metal substrates. Specifically, U.S. Pat. Nos. 3,705,857 and 3,762,953 to Clarke, Jr. et al use a combination of a dialkyl ketone and a solvent selected from dimethyl formamide, tetrahydrofuran and mixtures which the patentee indicates operates in a fast-acting manner for the express purpose of stripping coatings primed with polyvinyl butyral. Clarke et al, like many similar disclosures in the art at that time, reported that the application of the stripping composition resulted in the swelling of the coating due to the infiltration of the stripping solution, and the subsequent delamination of the coating from the substrate. The method according to Clarke et al U.S. Pat. No. 3,762,953 preferably took place within fifteen to thirty minutes, however, the resin under attack appears to break down and enter solution, with the remainder of the resin retaining a gel-like consistency resulting from the infiltration of the solvent. There is therefore no appreciation in the Clarke et al patents or anywhere in the prior art that the resin coatings might be capable of recovery to a state useful for recycling into subsequent commercial applications.
Other patent references were considered, all of which deal generally with the area of solvent stripping. These patents are listed serially below:
______________________________________ U.S. Pat. No. Patentee Date ______________________________________ 3,730,194 Shoner 1973 Re 27,432 Torrenzano et al 1972 3,475,218 Torrenzano et al 1969 3,429,823 Cataneo 1969 3,354,093 Early et al 1967 3,324,037 Rosenfeld 1967 3,321,407 Rosenfeld 1967 3,189,553 Lange 1965 3,179,609 Morison 1965 2,990,391 Grantham 1961 2,850,461 Bloch et al 1958 2,749,313 Williams et al 1956 2,610,166 Parry et al 1952 2,541,380 Polly et al 1951 2,435,239 Schub 1948 2,228,588 Rieche et al 1942 ______________________________________
Copies of the foregoing patent references have been forwarded herewith.
All of the above patent references relate primarily to solvent compositions whose express purpose is to attack the resin material and to drive it at least partially into solution to enable it to be removed from a non-resinous substrate. None of the references seeks to recover the resin in a form suitable for recycling or reuse in subsequent commercial applications.